Amazing tacos. Totally authentic. The menu is in Spanish but the staff speak English. Watch for the salsas - they are hot!
Another tip: if you want tacos, you need to be there during the first shift (before 9pm, I believe). Otherwise, they only make tortas. They're okay, but not as good as the tacos.
The butcher shop part of the store in the back seems a bit odd -- hardly any stuff in the refrigerator -- but adds to the unique ambience of the place.